SIDONOPS ANGULATA. 37 



for examination with high powers in a centrifugal spicule-preparation, I clearly 

 saw that a radial axial thread, extending right up to its end, is contained in each 

 ray. In the centre of a young sterraster of var. orthotriaena a little cluster of 

 a few very small granules, l}'ing close together, was observed. In the centre 

 of a slightly heated, adult sterraster of the massive specimen of var. megana I 

 observed an apparently solid black sphere, 15 /t in diameter, from which black 

 rays radiated to some distance. Such a blackening has been observed several 

 times. It seems to show that the central part of the spicule contains more 

 organic substance than the superficial part, and that the axial threads of the 

 rays are distally silicified to a greater extent than proximally. 



The .distal, freely protruding parts of the rays are in normal sterrasters 

 every^vhere, except in the vicinity of the umbilicus, 4-5 /j- thick and provided 

 with a terminal verticil of usually four to six stout, blunt, and often somewhat 

 curved, lateral spines (Plate 15, figs. 5, 6). The distal ends of the rays sur- 

 rounding the umbilicus have a transverse section, elongated in a direction 

 radial to the umbilicus, usually 4-5 n broad and 6-7 /< long. They are generally 

 provided with from seven to nine lateral spines and also bear several spines on 

 their terminal face (Plate 16, figs. 1-3). The spines of these rays, which are 

 directed towards the centre of the umbilicus, are a little larger than the others 

 and often curved. 



Besides these normal sterrasters some abnormal ones, for which I propose 

 the term sterroids, were observed, chiefly in var. orthotriaena and the massive 

 specimen of var. megana. The most frequent kinds of abnormities met with 

 are sterrasters in which the distal ray-ends are thicker, as much as 6-9 fi in 

 transverse diameter, farther apart, and provided with a greater number of 

 spines than in the normal sterrasters. In some of these sterrasters single scat- 

 tered spines, similar to those forming the verticils on the rays, arise here and 

 there between the protruding distal ray-ends directly from the surface of the 

 solid centrum of the spicule. Much more rarely strongylosphaeraster-like sterr- 

 asters with relatively long, terminally rounded, protruding rays were observed. 

 In some of these the protruding ray-ends were smooth, in others densely 

 covered with small spines. 



The two specimens of var. megana were trawled at Station 2975 on February 

 12, 1889, in 34° 1' 30" N., 119° 29' W., depth 66 m. (36 f .) ; they grew on a bottom . 

 of gravel and broken shells; the bottom temperature was 73.9° (57° F.). The 

 specimen of var. microana was caught with the tangles at Station 4417 on April 

 12, 1904, near Santa Barbara Islands, S. W. rock Santa Barbara Island, N. 8° W., 



